Lamb mortality and clostridial disease

To determine the level and timing of lamb loss that occurs during the first year of life on a typical hill country sheep and beef farm in the central North Island of New Zealand and to determine how much of this loss can be prevented through vaccination against the five main clostridial diseases using a commercially available multivalent clostridial vaccine.

The study was conducted on a single commercial hill country sheep and beef farm in the central North Island of New Zealand, with a history of never vaccinating their stock against clostridial disease. Lambs were blocked on sex and randomly selected at docking into treatment (n = 1,705 lambs) and control (n = 1,709 lambs) groups. Treated lambs were vaccinated at docking and 4 weeks later with 1 mL of multivalent clostridial vaccine. Control lambs were not vaccinated. Different coloured ear tags were used to identify the lambs in the treatment and control groups. All lambs were counted at docking (October 2019) and at six other management event times between docking and when the replacement hoggets were set stocked for lambing (August 2020). The number of lambs sold between each management event, from each group was also counted. The difference in the number of lambs from one management event to another, minus the lambs sold between these events was regarded as the lamb losses for that period.

The total percentage of lamb losses from docking to pre-lamb was 4.8% (81/1,705) and 6.2% (106/1,709) in the vaccinated and unvaccinated lambs respectively OR = 0.75 (95% CI = 0.56-1.02; p = 0.06). Most lamb loss occurred in the period after docking, followed by the period between weaning and the first post-weaning drench. Less lamb loss occurred in the vaccinated lambs (27/1,705; 1.6%) after docking than in the unvaccinated lambs (66/1,709; 3.9%). This was mainly due to lower female lamb losses in the vaccinated (5/868; 0.6%) compared to the unvaccinated (38/868; 4.4%) group (p < 0.001).

Vaccination of lambs at docking and 4 weeks later, with a multivalent 5-in-1 clostridial vaccine was associated with a 23.6% (25/106) reduction in total lamb loss from docking to pre-lambing. In female lambs, vaccination was associated with an 87% (33/38) reduction in lamb loss after docking and a 37% (22/59) reduction over the total trial period.